Pneumatic antishock garment inflation activates the human sympathetic nervous system by abdominal compression

Abstract

New Findings r What is the central question of this study?What is the mechanism by which pneumatic antishock garments increase blood pressure? r What is the main finding and its importance?Direct recordings of sympathetic nerve activity revealed that pneumatic antishock garments activate a sympathetically mediated reflex increase in blood pressure by compressing the abdomen, but not the leg. This mechanism has never been shown previously.Pneumatic antishock garments (PASG) have been proposed to exert their blood pressureraising effect mechanically, i.e. by increasing venous return and vascular resistance of the lower body. We tested whether, alternatively, PASG inflation activates the sympathetic nervous system. Five men and four women wore PASG while mean arterial pressure (MAP), muscle sympathetic nerve activity (MSNA), heart rate and stroke volume were measured. One leg bladder (LEG) and the abdominal bladder (ABD) of the trousers were inflated individually and in combination (ABD+LEG), at 60 or 90 mmHg for 3 min. By the end of 3 min of inflation, conditions that included the ABD region caused significant increases in MAP in a dosedependent fashion (7 ± 2, 8 ± 3, 14 ± 4 and 13 ± 5 mmHg for ABD60, ABD+LEG60, ABD90 and ABD+LEG90, respectively, P < 0.05). Likewise, inflation that included ABD caused significant increases in total MSNA compared with control values [306 ± 70, 426 ± 98 and 247 ± 79 units for ABD60, ABD90 and ABD+LEG90, respectively, P < 0.05 (units = burst frequency × burst amplitude]. There were no changes in MAP or MSNA in the LEG-alone conditions. The ABD inflation also caused a significant decrease in stroke volume (−11 ± 3 and −10 ± 3 ml per beat in ABD90 and ABD+LEG90, respectively, P < 0.05) with no change in cardiac output. Neither cardiopulmonary receptor deactivation nor mechanical effects can account for a slowly developing rise in both sympathetic activity and blood pressure during ABD inflation. Rather, these data provide direct evidence that PASG inflation activates the sympathetic nervous system secondarily to abdominal, but not leg, compression.

Paradoxical Muscle Sympathetic Reflex Activation in Human Heart Failure

“…[8][9][10]12,17 However, the possibility that changes in venous pressure also stimulated or unloaded sympathoexcitatory mechanoreceptors located in the peripheral venous circulation 31,32 or (as suggested by data from a few healthy subjects exposed to substantially higher positive pressure) the abdomen cannot be excluded. 33 Regardless, the present observations during LBPP demonstrate the existence in HFrEF of a unique venous volume or pressure-dependent sympathetic excitatory reflex. Finally, subtle movement in the microelectrode position between interventions could have led to recording from an anticipated single unit during LBNP and a paradoxical single unit during LBPP.…”

“…30 If these 12 U-firing single units were extracted from the aggregate data, the ratio of anticipated to paradoxical responses to LBPP would be similar between HFrEF patients and controls. Further investigation is required to determine whether this novel discharge pattern represents the functional emergence of a specific population of cardiopulmonary mechanoreceptors with a higher pressure operating point and unique firing characteristics, or results (in the HFrEF cohort only) perhaps from stimulation of extrathoracic mechanoreceptors [31][32][33] by the rostral volume shift induced by LBPP.…”

Compression Garment-induced Leg Changes Increase Hemodynamic Responses in Healthy Individuals

“…Nonetheless, the CGs used in the current study are commercially available, making the results more applicable to real-life situations. Secondly, the COMPs were applied only at the lower body in the current study, whereas abdomen compression may affect hemodynamic responses via sympathetic nervous system activation [36]. Nonetheless, abdominal compression may affect breathing patterns, therefore its effectiveness was not the focus of the current study and design of sports CGs.…”

Differences in autonomic neural activity during exercise between the second and third trimesters of pregnancy

“…It may be that the increase in intra‐abdominal pressure during exercise becomes more prominent in late pregnancy than in earlier gestational periods. Increase in intra‐abdominal pressure is reported to stimulate sympathetic activity . In addition, the growing uterus in TM3 subjects increases intra‐abdominal pressure during exercise and restricts venous return, which may inhibit the physiological stimulation of the cardiopulmonary baroreceptor, thereby inhibiting parasympathetic activity .…”